1. Field
Example embodiments in general are directed to a waterproof housing for a magnetometer, a combination including a magnetometer within a waterproof housing and to a system and method for location and removal of unexploded ordinance underwater.
2. Related Art
Devices for locating magnetic objects and/or for detecting or measuring magnetic fields are well known. Such devices can include a plurality of magnetic sensor units having spaced-apart windings or coils that are mounted within a non-magnetic tubular housing. U.S. Pat. No. 4,163,877 to Schonstedt is an example of a prior art magnetic detector, hereafter referred to as a “magnetic locator”.
Saturable core (fluxgate) magnetic locators or gradiometers comprise at least two electrically matched field-sensing elements mounted on a non-magnetic structure such that their magnetic axes are, theoretically, precisely parallel or coaxial. The output signals of the two sensors are arranged such that they oppose each other. If the structure is oriented in any direction in a uniform magnetic field, the components of magnetic field existing at each sensor are equal, so that there is no resulting output signal from the combination of the two sensors.
If a magnetic object exists within the detection range of the instrument, the magnetic field will generally be stronger at one of the sensors than at the other sensor. As a result, the output signal of one sensor will be greater than that of the other, so a net difference signal will be produced that is indicative of the presence of the object.
FIGS. 1-6 are directed in general to characteristics of a conventional “fluxgate” magnetic locator (also known as a “magnetometer”) used for locating ferromagnetic objects such as corner markers, gas lines, septic tanks, steel pipes, unexploded ordnance, water/sewer lines and the like, a commercially-known example being the Model GA-52Cx magnetic locator by Schonstedt Instrument Company. FIG. 1 is a perspective view of a conventional magnetic locator. As shown in FIG. 1, the magnetic locator 10 includes a tubular housing 12 connected to a housing 14 of larger cross-dimensions. Housing 12 is formed of non-magnetic material, such as aluminum, and includes a pair of spaced, aligned flux-gate magnetic sensors, shown generally as “sensor A” and “sensor B” in FIG. 4.
Housing 14 is formed of aluminum and contains the electronics for exciting the sensors and for processing signals from the sensors. In use, the locator 10 can be grasped at a portion of housing 12 near housing 14, and the tip 16 of housing 12 is swept along the ground to detect a buried magnetic object, for example. An audible signal indicative of the detection of magnetic objects is produced by a loudspeaker as described hereinafter. Holes (not shown) in the end wall of housing 14 are provided for the transmission of sound from a loudspeaker to the exterior of the housing 14. The holes are covered by a shield 64 that is secured to the housing 14 via a mounting screw 72.
FIG. 2A is a partial front view of the housing 14 to show various control knobs, and FIG. 2B is an enlarged view of the dotted line circle in FIG. 2A. Referring to FIG. 2A, the housing 14 includes a volume control knob 20, an on/off/sensitivity control knob 22 (hereafter “sensitivity control knob 22”, shown in dotted circle) and a headset jack 24. FIG. 2B illustrates the off position and five (5) sensitivity positions of the sensitivity control knob 22. In an example operating configuration, sensitivity control knob 22 can be set to position 2 and the volume control knob 20 can be adjusted until the idling tone reaches a desired level. The magnetic locator 10 can be oriented in any direction without producing a significant change in the frequency of the tone from its idling frequency. Additionally, when using headphones plugged into jack 24, the volume control knob 20 has no affect on the output level of the audio signal.
FIG. 3 is a partial exploded view with the housing 14 removed. The magnetic locator 10 is powered by two alkaline 9-Volt batteries 40, such as alkaline or lithium batteries. The batteries 40 are carried in a battery holder 32 as illustrated in FIG. 3. Access to the batteries 40 is obtained by removing the two knurled nuts 56 and sliding off the housing 14.
FIGS. 4-6 describe the function and operation of the magnetic locator 10. The magnetic locator 10 detects the magnetic field of a ferromagnetic object. The magnetic locator 10 responds to the difference in the magnetic field between two sensors A, B spaced about 20 inches apart. The response is a change in the frequency of the signal emitted by the piezoelectric speaker. FIG. 4 shows an application of the locator 10 in which it is used to detect an iron marker of the type used for property line identification. As shown, the magnetic field of the iron marker is stronger at sensor A than it is at sensor B. As a result, the frequency from the piezoelectric speaker is higher than the idling frequency, 40 Hz, which exists when the field strength is the same at both sensors. Accordingly, as this magnetic locator 10 employs flux-gate sensors it is sometimes referred to as a “flux-gate magnetometer”.
To conduct the search, the user sets the sensitivity and adjusts the volume (or wears headphones), then grasps the tubular housing 12 above sensor B, generally near the front of housing 14 as shown in FIG. 5. Because the upper sensor B is located near where the locator 10 is usually held, wrist watches may produce unwanted changes in the tones frequency. The locator 10 is kept away from the shoes, since shoes might contain magnetic material. To obtain maximum area coverage, the locator 10 should be swept from side-to-side. When the locator 10 comes within range of an object, the holder or user will hear an increase in the frequency of the output signal.
FIG. 6 illustrates basic signal patters for vertical and horizontal targets. After the user has detected the presence of a target, the locator 10 is held vertically and moved back and forth in an “X” pattern. The peak signal occurs directly over a vertical target, and over the ends of a horizontal target, as shown in FIG. 6.
Detecting unexploded ordinance is one of the many applications of the magnetic locator 10, as noted above. Upon the closing of military bases during the first round of Base Realignment and Closure (BRAC) in the early 1990s, a new industry revolving around the removal of Unexploded Ordinance (UXO) and Munitions and Explosives of Concern (MEC) was born. Over the course of the next twenty years the industry matured but the basic principle to remove an anomaly in the ground remained the same; lay a grid over an area, have an Explosive Ordinance Disposal Technician (EOD Tech) walk systematically through that grid with a magnetometer, and dig any anomalies.
In January 2009 the Army Corps of Engineers let a solicitation to conduct a Time Critical Removal Action (TCRA) underwater at South Beach on the Island of Martha's Vineyard, Mass. The major obstacle to completing that work was the lack of a diver-held magnetometer that was waterproof. Conventional protocol and methodologies existed to clear land-based anomalies using magnetic locators such as the Model GA-52Cx. However, no protocol had been developed to search for and remove UXO and MEC underwater, no quality assurance (QA) check was possible, and conventional magnetic locators such as the GA-52Cx are not configured for underwater operations.